1. Field of the Invention
The principal object of this patent of invention is an anticorrosion terminal with short anchoring, without joint seams, for storage batteries, which contributes significant advantages resulting from its minimal corrosion due to migration of the interior electrolyte, from its appreciably lighter weight than the terminals fabricated up to the present, and from the reduced maintenance required during operation of batteries in which the said terminal is used.
More specifically, this patent of invention covers a terminal of the type specified for its use in storage batteries, which has been conceived and developed as a result of experience acquired in the use of these devices to generate electrical energy, and of laboratory tests dedicated to studying the highly harmful process of corrosion of lead alloy terminals, generated by the migration of the electrolyte toward the outer metal surface during the battery's operation. In this sense, the invented terminal reduces such migration to a minimum and, consequently, its outer surface remains clean, preserving a good electrical contact with the terminal of the external circuit to which it is connected. Likewise, the aforementioned substantial diminution of the corrosion permits operation of the battery practically without the need for the customary maintenance tasks of cleaning the terminal. Furthermore, as it contains a lesser amount of material than the terminals used up to the present, it is appreciably lighter, with the additional advantage of lower production costs due to the savings of material and simplicity of the tools used in its manufacture.
2. Description of the Prior Art
As is known, the storage battery comprises a case--generally of thermoplastic material--receiving the electrolyte and the lead plates of positive and negative polarity. In its upper portion, this battery has a top or cover--also of thermoplastic material--through which project, in most battery designs, the upper portions of two lead terminals. This upper portion may take on several configurations, but it is generally constituted by a hollow body forming a frustum of cone whose dimensions are established by the DIN, SAE, SETIA and other standards. In the vicinity of its lower end of greater diameter, this hollow frustum of cone is prolonged in a lower portion, also hollow, which is embedded in the thermoplastic material, and constitutes the portion of the terminal intended for its anchoring in the top or cover. Furthermore, the interior cavity of the upper frustum of cone body and the lower portion of such terminals form the space for housing each of the rods connected respectively to the inside plates of positive and negative polarity.
Each interior rod is connected at or near its upper end to the respective lead terminal by means of a weld using lead or an alloy of this metal, thus achieving the necessary electrical continuity.
As is known, the advanced technology of battery manufacture consists in using injector machines, by means of which the thermoplastic material is injected into the mold which forms the top. In a preliminary operation, the terminals are positioned, manually or automatically, in respective orifices of the mold, and after injection of the molten plastic material at high pressure, the terminals remain adhering to the top by means of their lower portion, partially embedded in the thermoplastic material.
The battery manufacturers and end-product motor vehicle companies set the minimum axial stress and torque which each terminal must withstand without producing a rupture in the metal and/or thermoplastic material of the top. For purposes of satisfying this mechanical securing requirement, several designs for the terminal's lower portion have been developed, all of which assure the anchoring of the lower portion in the top's material.
These designs consist, in general, of a number of circumferential and parallel projections which impede axial displacement, while the means blocking rotary movement may have different configurations, such as a number of cavities into which flows the injected plastic material and which are formed in the perimeter of the side wall, or also a number of projections or teeth which are projected radially, etc. Examples of the configuration of these means to anchor the lower portion of the terminal, can be seen in the drawings of patents U.S. Pat. No. 5,296,317 and EP 261.311.
As can be seen in the cited patents of invention, the configuration of the lower portion of the terminal is such that in the process of manufacturing this metal element, it is necessary to use dies--in the case of cold process stamping and pressure diecasting, or molds--in the case of blast furnace tapping--which, once the piece has been furnished, and owing to its configuration, must be opened horizontally, that is, perpendicular to the terminal's axis of symmetry, in order to remove it from its lodging cavity in the implement. These molds or dies, then, must be constituted of two or more movable parts which once displaced radially, leave burrs or joint seams in the material of the lateral surface of the lower portion of the formed terminal, parallel to its axis of symmetry, and the material's surfaces face and come into contact with the adjacent parts of the die or mold. The thickness of these burrs or joint seams increases as the die or mold ages, as a consequence of the continuous opening and closing of its components.
Tests made with penetrating ink have disclosed that these burrs or joint seams constitute paths through which the electrolyte flows to the outside, causing corrosion of the terminal, to which it adheres. This migration of the electrolyte through the burrs or joint seams is compounded by the capillary migration generated by the internal porosity of the lead alloy, when the terminal is manufactured by means of tapping or pressure diecasting processes.
All of the terminals used up to the present in tops or covers of thermoplastic material for batteries satisfy the aforementioned mechanical anchoring or securing requirement by means of a lower portion embedded in the top, the formation of which requires the use of molds or dies, which must necessarily be opened by displacing their constituent parts perpendicularly to the terminal's axis of symmetry for its extraction after it has been formed. These terminals, in addition to the drawback of having the longitudinal burrs or joint seams, which strongly influence the corrosion process of their outer surface, incur the additional problem that their lower portion--whose length may be as much as 1/3 of the terminal's total length--possess a quantity of lead alloy, which not only lacks function from the electrical point of view, but also unnecessarily adds to the total weight of the terminal.